import

Using your approach, I think it would be less time consuming and avoid some potential errors if you simply created a new catalog (from the File>Manage Catalogs dialog) rather than delete files from the old catalog.  

Once everything is up and running you can delete the original catalog folder. 

However, before doing that, you might try just importing files from the Pictures folder.  In theory, Elements will only import files that aren't already in the catalog from the OneDrive folder. 

Just to be clear, the Organizer does not store copies of the photos, it merely creates a database of where they are currently stored.  So, if you import from both parent folders, there will be no new photo files created.  The Organizer will contain a single reference to the first file it imports and will reject any true copies that are imported from a different folder.

Now, as I say, no duplicates should find their way into the catalog.  But as Yogi Barra said:  In theory, there is no difference between theory and practice - in practice, there is.